Focused medical surveillance: a search for subclinical movement disorders in a cohort of U.S. workers exposed to low levels of manganese dust.

Seventy-five workers with recent and/or historical exposure to manganese (Mn) at a metal producing plant in northern Mississippi were closely matched with 75 control workers who had no known history of occupational exposure to Mn. Both plants are OSHA STAR work sites and share common medical, safety, and industrial hygiene services. Airborne Mn levels were assessed for each of twelve job categories at the Mn facility by collecting 63 side-by-side full-shift personal samples of both total and respirable Mn dust. Exposures of workers currently working with Mn averaged 0.066 mg/3 respirable and 0.18 mg/3 total Mn. An assessment of major equipment and work practice changes over the past several years and estimates of the resultant relative impacts on exposure was made. Based on this information and individual employment information, each worker's cumulative exposure to respirable and total Mn was estimated for the preceding 30 days, preceding year, and for the worker's entire employment history. Both Mn and control workers were administered multiple neuropsychological tests including tests of hand-eye coordination, hand steadiness, complex reaction time, and rapidity of finger tapping. A questionnaire was used to evaluate a worker's neuropsychological status. Performance decreased significantly with increasing age in tests of hand-eye coordination, complex reaction time and finger tapping speed. No effect of Mn exposure was found on the results of the questionnaire or any neuropsychological test.

Evaluation of a population with occupational exposure to airborne ammonium perchlorate for possible acute or chronic effects on thyroid function.

Employees at an ammonium perchlorate production facility in Nevada and a larger control population from the same chemical complex without direct AP exposure were monitored extensively for airborne perchlorate exposure. Single-shift and working-lifetime cumulative dose estimates were made using standard breathing-rate estimates and assuming rapid absorption, based upon solubility. Calculated single-shift doses ranged from 0.2 to 436 micrograms/kg, with an average of 36 micrograms/kg. Working-lifetime cumulative doses in the higher exposure group ranged from 8,000 to 88,000 micrograms/kg, with an average of 38,000 micrograms/kg. Thyroid profiles, including free thyroxine index and thyroid-stimulating hormone level, were obtained both before shift and after shift to assess thyroid-axis perturbation due to single working-shift perchlorate exposure. Thyroid-function data were also analyzed with respect to estimates of cumulative exposure to assess any measurable chronic effects on thyroid gland function. Additionally, standard clinical blood test parameters of liver, kidney, and bone marrow function were evaluated to assess any measurable chronic effects of perchlorate exposure on those organs. Multiple regression was used to assess the effects of exposure variables and demographic variables on organ function parameters. No perchlorate-attributable effects on thyroid, bone marrow, kidney, or liver function were detected.